Blood collection is always important, particularly in times of emergency (immediate use), but whole blood may only be stored for about 30 days before it is “outdated”. For long term storage, the ability to separate the whole blood into its major components (white blood cells, platelets, red blood cells and plasma) is of paramount importance because the long term storage conditions for each component is different in terms of temperature and storage media. The most important component separations occurring after collection is the separation of red blood cells (RBC), white blood cells (WBC), platelets, and plasma from one another. Within the WBC it is sometimes important to separate the granulocytes from the lymphocytes. After separation and extraction of particular components, a fraction of the blood may be returned to the patient.
It is possible to separate the various components of whole blood either under or after centrifugation, due to their differing densities. Some prior art methods, such as that in U.S. Pat. No. 4,120,448, utilize a chamber connected to a centrifuge. The centrifuged blood separates in the chamber, and a plurality of collection means are positioned at various locations in the chamber corresponding to the areas where each component congregates, which is density-dependent.